102 research outputs found
Complementary experimental methods to obtain thermodynamic parameters of protein ligand systems
In recent years, thermophoresis has emerged as a promising tool for
quantifying biomolecular interactions. The underlying physical effect is still
not understood. To gain deeper insight, we investigate whether non-equilibrium
coefficients can be related to equilibrium properties. Therefore, we compare
thermophoretic data measured by thermal diffusion forced Rayleigh scattering
(TDFRS) (which is a non-equilibrium process) with thermodynamic data obtained
by isothermal titration calorimetry (ITC) (which is an equilibrium process). As
a reference system, we studied chelation reaction between
ethylenediaminetetraacetic acid (EDTA) and calcium chloride (CaCl) to
relate the thermophoretic behavior quantified by the Soret coefficient
to the Gibb's free energy determined in the ITC
experiment using an expression proposed by Eastman [J. Am. Chem. Soc. 50, 283
(1928)]. Finally, we have studied the binding of the protein Bovine Carbonic
Anhydrase I (BCA I) to two different benzenesulfonamide derivatives:
4-fluorobenzenesulfonamide (4FBS) and pentafluorobenzenesulfonamide (PFBS). For
all three systems, we find that the Gibb' free energies calculated from
agree with from the ITC experiment. In addition, we
also investigate the influence of fluorescent labeling, which allows
measurements in a thermophoretic microfluidic cell. Re-examination of the
fluorescently labeled system using ITC showed a strong influence of the dye on
the binding behavior
Calculation of Three-dimensional Energy Product for Isotropic Nd2Fe14B Magnet
A conventional energy product calculated by the product of the B-field and the H-field is not sufficient for representing the performance of a magnet because it considers the homogeneous and only the uniaxial magnetic properties of the magnet. The conventional energy product has been compared with another energy product obtained by integrating the scalar product of the B-field and the H-field of each cell composed of the three-dimensional components. We investigated a model system by micromagnetic simulation using finite differential method (FDM) and calculated the full hysteresis of the magnet. The model system of a Nd2Fe14B magnet composed of grains with a diameter of about 100 nm was assumed. In the case of the isotropic multi-grain magnet, the energy product calculated by the integration method was 28% larger than the energy product obtained by the conventional way, although a discrepancy between the distribution of the magnetizations and the demagnetizing fields at the reversal process resulted in the decrease of the energy product
Tuning of oscillation modes by controlling dimensionality of spin structures
Harmonic oscillation of spin structures is a physical phenomenon that offers great potential for applications in nanotechnologies such as nano-oscillators and bio-inspired computing. The effective tuning of oscillations over wide frequency ranges within a single ferromagnetic nanoelement is a prerequisite to realize oscillation-based nanodevices, but it has not been addressed experimentally or theoretically. Here, utilizing a vortex core structure, one of spin structures, we report a drastic change of oscillation modes over the frequency range from MHz to sub-GHz in a 100???nm-thick permalloy circular disk. Oscillation mode was found to considerably depend on the shape and dimension of the vortex core structure and various oscillation modes over a wide range of frequencies appeared with dimensional change in the vortex core structure. This work demonstrates that oscillation modes of the vortex core structure can be effectively tuned and opens a way to apply spin structures to oscillation-based technology
Thermophoretic Micron-Scale Devices: Practical Approach and Review
In recent years, there has been increasing interest in the development of micron-scale devices utilizing thermal gradients to manipulate molecules and colloids, and to measure their thermophoretic properties quantitatively. Various devices have been realized, such as on-chip implements, micro-thermogravitational columns and other micron-scale thermophoretic cells. The advantage of the miniaturized devices lies in the reduced sample volume. Often, a direct observation of particles using various microscopic techniques is possible. On the other hand, the small dimensions lead to some technical problems, such as a precise temperature measurement on small length scale with high spatial resolution. In this review, we will focus on the “state of the art” thermophoretic micron-scale devices, covering various aspects such as generating temperature gradients, temperature measurement, and the analysis of the current micron-scale devices. We want to give researchers an orientation for their development of thermophoretic micron-scale devices for biological, chemical, analytical, and medical applications.Keywords: microfluidic; thermophoresis; thermodiffusion; temperature gradients; temperature measurement
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